Wireless receiving circuit



M. M. PHILLIPS WIRELESS RECEIVING CIRCUIT June 19, 1928, 1,674,448

Filed March 20. 1926 m MINI I11: I i

INVENTOR Patented June 19, 1928.

UNITED STATES 1,674,448 PATENT OFFICE.

MAURICE M. PHILLIPS, 0F PITTSBURGH, PENNSYLVANIA.-

WIRELESS RECEIVING CIRCUIT.

Application filed March 20, 1926. 7 Serial No. 96,186.

This invention relates to improvements in wireless receiving circuits and more particularly to improvements in circuits employing the heterodyne method of reception.

One object of this invention is to so couple a directional bridged collector circuit with a bridged oscillating detect-or circuit that the two circuits will function so that a receiver employing the same will cover the entire broadcast range from 545,000 cycles to 1,500,- 000 cycles, will require but two main variable tuning condensers and will not reradiate.

This and other objects which will appear to those skilled in this art are attained by means of the circuit arrangement which is diagrammatically illustrated in the single sheet of drawings accompanying and forming part of this application.

In a general way the circuit system includes two bridged circuits and means for coupling these bridged circuits together. One of the bridged circuits includes a directional loop, a three-element vacuum tube, a variable capacity for tuning the circuit to carrier frequency and a variable capacity for balancing or neutralizing the inherent grid plate capacity of the vacuum tube and the wiring associated therewith, The other circuit which includes a three-element vacuum tube serving as an oscillating detector also includes a variable capacity for determining the frequency of the locally generated oscillating current used for heterodyning.

The bridged circuit which operates as the collector circuit is balanced or neutralized in a manner similar to the method disclosed in Hazelt-ine Patent No. 1,450,080, of March 27, 1923, while the other bridged circuit embodies the principle disclosed in Pressley Patent No. 1,560,854, of Nov. 10, 1926.

The coupling device between these bridged circuits which serves to transfer the collected signals from one circuit to the other, consists of two aperiodic inductances of suitable value, magnetically coupled together. The output circuit of the bridged collector is conductively coupled to one of these aperiodic inductances, while the input circuit of -the bridged oscillating detector is conductively coupled to the other aperiodic inductance.

These aperiodic inductances preferably take the form of an iron core radio frequency transformer.

For the purpose of completely disclosing my: invention and in order to facilitate its practical application by those skilled in the art, I give below a detailed description of a part of a circuit system embodying this invention and which may be utilized in a receiver in connection with intermediate frequency and audio frequency amplifiers of any standard form. p

Referring to the drawings, more particularly by referencenumerals and letters, the loop L which will preferably be mounted so asto be capable of being rotated to different positions istapped at its exact center and is connectedup by means of leads 2 and 2 to the center arm 3 of a variable resistance T Whichis preferably in the form of a potentiometer. Thisresistance is connected across a battery or other current-supply A and servesas a throttling device. I

The loop L forms two inductive arms of'a bridge and the inner ends (junction point) of these inductive arms are connected to lead 2. The other end 4 of one of the inductive arms is connected to the grid 5 of a vacuum tube 6, while the outer end 7 of the other inductive arm of the bridge L is connected to plate 8 of the tube 6 through a variable capacity 9. Variable capacity 9, must be of such value as to be capable of equaling or balancing the inherent capacity existingbetween the grid 5 and plate 8 (and the connected wiring) of vacuum tube 6.

10 represents a variable capacity connected across loop L and of suitable value to tune loop L to the frequency desired.

The variable. resistance T whichv 1 term the throttle isconnected across the filament battery and conductively couples the bridged collector circuit to the bridged oscillating detector circuit through inductance 12.

The bridged collector circuit is most sensitive when its grid circuit is negatively biased, and negative biasing is accomplished. by. swinging the center arm 3' of variable resistance T toward the negative potential of the A battery. In balancing the bridged collector circuit it is highly desirable to swing center arm 3'to its full negative position.

Upon receiving a strong signal. from a nearby transmitter the tendency of theoscillating detector circuit to become blocked can be corrected and as I'term it, throttled out, by swinging arm 3 of the variable resistance T toward the positive potential of the A battery. This blocking tendency be capacity 21 to the negative side of comes greater as the frequency of the re ceived signal increases and less as the frequency decreases.

Plate 8 of tube,6 is connected to one end of an inductance 11, the other end of the inductance being connected to the positive side of a batterv B which is utilized to supply current to plate 8.

Inductance 11 is preferably the primary winding of an iron core aperiodic radio frequency coupling transformer so designed as to be suitable for present day broadcasting reception. 12 represents the secondary WlIl(l ing of said coupling transformer and is conductively coupled to the junction point 13 of inductances 14 and 15, while the open end 16 of inductance 12 is connected to movable arm 3 of throttle T. p

1 1 and 15 are preferably of toroidal form and are preferably formed by tapping the secondary of a toroidal coil of suitable in ductance at its exact center, thus forming two equal inductive arms. ,The outer end 16 OflndUCtlVG arm .14: is'connected to the grid 17 of a three element vacuum tube 18 through a suitable resistance 19 and capacity 20 (preferably 100,000 ohms and .00025 M. F. D. respectively). Outer end 16 of inductive arm 14 is also connected through a fixed the filament 22 of vacuum tube 18.

The outer end 28 of inductive arm 15 is connected to the negative side of filament 22 through a suitably valued variable capacity 2 1.'-

The value of fixed capacity 21 is prefer ably .00008 M. F. D. and the value of va riable capacity 24 is preferably .000045 M. F. D. A Variable capacity '25 is connected across inductive arms 14 and 15 and functions to produce the desired frequency of the locally generated oscillations. The capacity of 25 is such as to tune the inductive arms i 14 and 15.

Inductive arms I l-and 15 and the capacity arms (in one instance including the fixed capacity 21 and in the other, variable capaci other end'of inductance 31 is connected to the positive side of battery B. Inductance 32 forms the input circuit of an 1ntermediate amplifier and second'detector commonly used to amplify the output of a hetero dyne circuit. A by-pass condenser 32 may be utilized as a plate to ground filter. v

Having thus described my invention What I claim as new and desire to secure by'Lettcrs Patent is:

1. A circuit system comprising a bridged collector circuit which includes two induc tive arms a three element vacuum tube and a capacity for balancing the inherent grid plate capacityof said tube, a second bridged circuit which includes two inductive'and .tWo capacity arms and a three element vacuum tube and two inductances magnetically coupled together and conductively coupled to said circuits.

A. circuit system comprising a directional bridged collector circuit, which includes a directional loop, a three element vacuum tube and a variable capacity for balancing the inherent grid plate capacity of said tube, a second bridged circuit which includes two inductive and two capacity arms and a three element vacuum tube which functions as an oscillating detector and two inductances magnetically coupled together and conduotively coupled to said circuits.

In testimony whereof, I have hereunto subscribed my name this 18th day of March, 1926.

MAURICE M. PHILLIPS.

25 of vacuum tubes 

